SAMSUNG M393B5170EH1-CH9 4GB DDR3 PC10600 240P DIMM at Amazon.com
48GB (3X 16GB) Matched Pair 1333MHz 240-Pin SDRAM DIMM DDR3 (PC10600) Memory Upgrade Kit for PC Desktops, Mac Pro 'Nehalem' & 'Westmere' (OWC1333D3X9M048) at Amazon.com
Amazon.com: OWC 128GB (4 x 32GB) PC10600 DDR3 ECC-R 1333MHz DIMMs Memory Compatible with Mac Pro Late 2013 Models (OWC1333D3Z3M128) : Everything Else
SAMSUNG M393B4G70BM0-YH9 32GB SERVER DIMM DDR3 PC10600(1333) REG ECC 1.35v 4RX4 240P 4GX72 2GX4 CL9 at Amazon.com
OWC 8.0GB DDR3 ECC-R PC10600 1333MHz SDRAM Memory Upgrade Module Compatible with Mac Pro 2009-2012 (OWC1333D3MPE8GB) at Amazon.com
48GB (3X 16GB) Matched Pair 1333MHz 240-Pin SDRAM DIMM DDR3 (PC10600) Memory Upgrade Kit for PC Desktops, Mac Pro 'Nehalem' & 'Westmere' (OWC1333D3X9M048) at Amazon.com